I've only decided to jump off once, and then another time elected to stay off after I fell.
The time I ditched was because my girth was NOT tightened (I take complete and total responsibility, taught me to never rush through tacking up) and my saddle was slipping under my mare's belly. We were turning a corner rather sharply and then BAM! I'm sideways. Unfortunately, we were also cantering, and I couldn't really stop. Ended up yelling "WOAH!", pulling my foot out of the stirrup and supermanning my way into the dirt. I got up, looked over, and Rainy just sorta stood there, looking at me like "Why'd you jump off? I stopped."
I felt more than a little dumb.
The second situation was on the oddest horse I've had to ride. He was my starter show horse, a super slow Quarter horse that would barely move an inch walking, but would spook and shy at just about anything. After a lesson, two other girls and I went out to cool off on trails. We were crossing a small ditch, with myself in back, and the middle horse refused to move. As the front girl turned her horse around to help, a deer sprinted out across the trail ahead of us. My horse spooked, frightening the middle horse, which frightened the front horse. I wasn't expecting it at all (this was the first, but sadly not the last, time he spooked with me) and flew off. Since we were nervous, thinking there might be more deer out, we decided to all dismount and handwalk back.
There are my stories! :) When you think you're going to ditch, just picture in your head what you want to happen on the horse, not off of it. So if the footing to a jump is funky, instead of thinking you're going to fall off, picture yourself clearing the jump and cantering away safely. :) Hope that helps, even just a little bit.